The cortistatins are a group of anti-angiogenic steroidal alkaloids first isolated in 2006 from the marine sponge Corticium simplex. See, e.g., Aoki, et al., JACS (2006) 128: 3148-9. From the date of isolation to the present, these natural products have been the subject of much study, especially in the development of total syntheses and of new unnatural biologically active analogs. See, e.g., Aoki et al., Bioorganic & Medicinal Chemistry (2007) 15: 6758-62, Mousseau et al., Cell Host & Microbe (2012) 12: 97-108; Chen et al., Organic & Biomolecular Chemistry (2010) 8: 2900; Hardin et al., European Journal of Organic Chemistry (2010) 19: 3553. Thus, there is an active interest in the development of new cortistatin analogs and methods of their preparation.